The present invention relates to a surface acoustic wave element, in particular to a surface acoustic wave element such as a surface acoustic wave filter used for mobile communication. Further, the present invention relates to a surface acoustic wave element suitable for flip-chip assembling and a surface acoustic wave device in which a surface acoustic wave element is mounted on a package, in particular to a surface acoustic wave device such as a band pass filter in microwave stage in which a surface acoustic wave element is flip-chip assembled.
Recently, surface acoustic wave elements such as surface acoustic wave filters are much in use in mobile communication in which demand for miniaturization is strong. For this use, a piezoelectric substrate thereon a surface acoustic wave filter is formed is adhered to the inside of a ceramic package, and signal input/output terminals disposed inside of the package and bonding pads on the piezoelectric substrate are connected with bonding wires consisting of Au, Al or the like to mount. Thereafter, a metal cap is put thereon and welded to a metal frame at the upper portion of the package, thereby hermetic sealing the surface acoustic wave element in the package.
The signal terminal in the package is communicated with an external terminal of the package through a via-hole or a castellation. The package is mounted on for instance a printed wiring board, external circuit and the external terminal of the package being connected. Thus formed surface acoustic wave filter, being capable of surface mounting on a printed circuit board during assembling, can be assembled with high density. Accordingly, the surface acoustic wave filters thus formed are components suitable in miniaturizing an electronic instrument such as portable telephones or the like.
There is flip-chip assembly technique that is recently used as an assembly technique capable of further miniaturizing a surface acoustic wave element. In the flip-chip assembly technique, a surface acoustic wave element is face down bonded on a package called an envelope. In the flip-chip assembly technique, conductive bumps are formed of Au or the like on portions where electrical connection of the surface acoustic wave element is necessary, which is put opposite on a printed circuit board of the envelope thereon conductive patterns are formed, followed by heating or ultrasonic inputting to connect.
The conductive pattern of the printed circuit board is connected to an external terminal disposed on a bottom surface of the printed circuit board. After thus mounting the surface acoustic wave element on the envelope, a cap is put on the envelope to hermetic seal the surface acoustic wave element.
Thus, in the flip-chip assembly technique, since the bonding wire is not used, a portion for wire bonding is not necessary on the package. Further, in bonding due to the wire bonding, there is a necessity of ensuring an excess space in the envelope for introducing a tool that introduces the bonding wire and connects with the bonding pad. On the contrary, in the flip-chip connection, the bonding tool is not necessary to result in cutting down the excess space.
Thus, the flip-chip assembly technique is an assembling method suitable for miniaturization of a surface acoustic wave device.
A surface acoustic wave filter, having a steep rise frequency characteristic, is a device of excellent frequency selectivity suitable for the case where high attenuation characteristic is necessary particularly in the neighborhood of a pass band.
However, in the surface acoustic wave filter, in a frequency band far apart from the pass band, the frequency characteristics of the surface acoustic wave filter are largely affected by stray capacitance of the package thereon the surface acoustic wave element is mounted, inductance of bonding wire, mutual inductions between a plurality of bonding wires or the like. Accordingly, there are problems that attenuation characteristics intrinsic to the surface acoustic wave filter cannot be sufficiently obtained.
Accordingly, when for the surface acoustic wave filter, attenuation characteristic in a frequency band far apart from a pass band is demanded, a technique that another resonant system is formed in the surface acoustic wave device and a trap due to the resonant system is fitted in a frequency band far apart from the pass band has been frequently used.
With such a configuration, the surface acoustic wave filter, when used for a portable telephone for instance, can improve the attenuation characteristics at a frequency band of a local oscillator or image frequency that are apart from a transmitting band or a receiving band.
Usually, these bands are frequency bands several hundreds MHz apart from the pass band. At that time, to form a trap of a surface acoustic wave filter, a resonant system due to inductance of the bonding wires and that of routing electrode pattern, and stray capacitance in the package and that of the routing portion has been mostly used.
As mentioned above, to advance miniaturization of the surface acoustic device, the flip-chip assembly technique is preferably adopted. When flip-chip mounting is implemented, however, due to an absence of the bonding wire, there is no inductance pertaining to the bonding wire. In addition, in flip-chip assembling, the bump connecting between the surface acoustic wave element and the envelope has a magnitude of approximately several tens xcexcm. As a result, compared with the bonding wire, the inductance is remarkably small. Accordingly, it was difficult to obtain a resonant system that forms a trap in a frequency band several hundreds MHz apart from the pass band due to inductance of the bump and that of the routing electrode pattern, and stray capacitance in the package and that of the routing portion.
In the case of the flip-chip assembling being adopted, there is no mutual induction between the bonding wires. As a result, there is an advantage that characteristics in a broad band, particularly in a high frequency region of 3 GHz or more, can be improved. Despite that, it is difficult to obtain an attenuation region such as the trap in the frequency band approximately several hundreds MHz apart from the pass band. As a result, there are problems that the flip-chip mounted surface acoustic wave devices cannot be used in various kinds of mobile communication systems including portable telephones, PHSs or the like.
The present inventions were carried out to solve these problems.
That is, an object of the present invention is to provide a surface acoustic wave element that can be miniaturized and can be improved of characteristics out of band.
Another object of the present invention is to provide a surface acoustic wave device that even when flip-chip assembling a surface acoustic wave element, can achieve both the miniaturization and the improvement of characteristics out of band. In particular, the object is to provide a surface acoustic wave filter having high attenuation characteristics even in a frequency band several hundreds MHz apart from a pass band.
Still another object of the present invention is to provide a surface acoustic wave element capable of adjusting attached capacitance with a high degree of freedom.
Still another object of the present invention is to provide a surface acoustic wave element that has large mechanical strength at a bump formation portion suitable for the flip-chip assembling and a structure of high connection reliability.
In order to solve these problems, the present invention adopts a configuration described in the following.
A surface acoustic wave element of the present invention comprises a piezoelectric substrate and a two-port surface acoustic wave resonator filter having input IDT (interdigital transducer) and output IDT. Here, one of a pair of interdigital electrodes constituting the input IDT is connected to an input side signal conductive pattern including an input side signal wiring and an input signal terminal, the other one being connected to an input side ground conductive pattern including an input side ground wiring and an input side ground terminal. One of a pair of interdigital electrodes constituting the output IDT is wired to an output side signal conductive pattern including an output side signal wiring and an output signal terminal, the other one being connected to an output side ground conductive pattern including an output side ground wiring and an output side ground terminal. At least one of the input side and output side ground conductive patterns is extended facing to both the input side and output side signal conductive patterns to form capacitance.
In the present surface acoustic wave element, between at least one of the input side and output side ground conductive patterns on the piezoelectric substrate and both the input side and output side signal conductive patterns, capacitances are formed to couple. The other ground conductive pattern, if it is an input side, may be formed to have capacitance with the output side signal conductive pattern, and if an output side, may be formed to have capacitance with the input side signal conductive pattern.
For the two-port surface acoustic wave resonator filter of the present surface acoustic wave element, a longitudinal mode coupled type surface acoustic wave resonator filter having three or more IDTs may be used.
That is, in the present surface acoustic wave element, at least one of ground conductive patterns including wiring and ground terminal connected to the interdigital electrodes of the IDT constituting the two-port surface acoustic wave resonator filter and both input and output signal terminals of the two-port surface acoustic wave resonator filter are disposed to couple through capacitances.
By adopting such a configuration, a resonant system having a trap in a frequency band apart from a pass band of the filter, for instance in a frequency band separated by several hundreds MHz, can be added. Accordingly, even when a surface acoustic wave element is flip-chip connected on for instance an envelope to mount, characteristics out of band can be improved and an adjustment of characteristics in conformity with a communication system can be implemented.
The capacitances between at least one of the input side and output side ground conductive patterns of the two-port surface acoustic wave resonator filter and both the input and output signal terminals can be formed by the following means.
These capacitances may be formed by disposing for instance the ground conductive pattern so as to face the input/output conductive patterns. Alternately, these may be formed due to comb-shaped capacitive electrodes. Further, on the piezoelectric substrate, a plurality of conductor layers may be disposed to face to each other through layers of dielectrics.
That is, in the surface acoustic wave element of the present invention, at least one of the input side and output side ground conductive patterns of the two-port surface acoustic wave resonator filter comprises at least one of an input capacitance formation conductive pattern and an output capacitance formation conductive pattern. The input capacitance formation conductive pattern is part of the ground conductive pattern and is extended facing to the input side signal conductive pattern and the input side signal conductive pattern. The output capacitance formation conductive pattern is part of the ground conductive pattern and is extended facing to the output side signal conductive pattern and the output side signal conductive pattern. Here, at least one of capacitances between the ground conductive pattern and the input side signal conductive pattern and between the ground conductive pattern and the output side signal conductive pattern can be formed between the signal conductive pattern and the capacitance formation conductive pattern extended facing to the output side signal conductive pattern.
In the surface acoustic wave element of the configuration, from at least one of ground terminals thereof, conductive pattern is connected on the piezoelectric substrate, and the conductive pattern, by disposing close to both wiring patterns connected to the input signal terminal of the two-port surface acoustic wave resonator filter and a wiring pattern connected to the output signal terminal, forms electric capacity therebetween. More specifically, the ground conductive pattern is routed (extended) approximately in parallel with the routing portions of the input/output side signal conductive patterns each, thereby a desired capacitance being formed.
Further, in the present surface acoustic wave element, at least one of the input side and output side ground conductive patterns of the two-port surface acoustic wave resonator filter comprises comb-shaped capacitive electrode for at least one of with the input side signal conductive pattern and with the output side signal conductive pattern, at least one of capacitances between the ground conductive pattern and the input side signal conductive pattern and between the ground conductive pattern and the output side signal conductive pattern being able to form by the comb-shaped capacitive electrodes.
In the configuration, due to the comb-shaped capacitive electrodes, between the ground electrode side of the two-port surface acoustic wave resonator filter and the input/output of the two-port surface acoustic wave resonator filter, electric capacity is formed.
When using the configuration, so that the comb-shaped capacitive electrodes do not excite surface acoustic waves to disturb signals, a pitch of the comb-shaped electrode and a direction of the comb-shaped pattern can be selected.
According to the configuration, compared with the case of forming capacitance due to a conductor pattern, the capacitance can be formed in a smaller area and a magnitude of added capacitance can be easily adjusted.
In the surface acoustic wave element of the present invention, at least on one ground conductive pattern of the two-port surface acoustic wave resonator filter a layer of dielectrics is formed, thereon at least one capacitance formation conductive pattern connected to the input side signal and output side signal conductive patterns being formed through the layer of dielectrics facing to the ground conductive pattern, at least one of capacitances between the ground conductive pattern and the input side signal conductive pattern and between the ground conductive pattern and the output side signal conductive pattern being able to form from the ground conductive pattern and the capacitance formation conductive pattern formed on the layer of dielectrics.
In the configuration, by interposing the layer of dielectrics between a plurality of conductor layers, between the ground terminal of the two-port surface acoustic wave resonator filter and the input and output signal terminals of the two-port surface acoustic wave resonator filter, capacitances are formed.
Due to strong demand for miniaturizing a surface acoustic wave element, an improvement of degree of freedom in designing is a serious concern. According to the aforementioned configuration, a magnitude of the capacitance to be formed can be adjusted with a larger degree of freedom, an adjustment of the position of the trap or the like being easily implemented.
Other than these, by disposing a conductor layer for instance on the envelope thereon a surface acoustic wave element is mounted in face down bonding, between the conductor layer and input/output IDT electrodes of the two-port surface acoustic wave resonator filter, capacitance may be formed.
Next, a surface acoustic wave device of the present invention is one formed by flip-chip assembling the aforementioned surface acoustic wave element of the present invention on a package called envelope due to face down bonding.
A surface acoustic wave device of the present invention comprises a piezoelectric substrate, a surface acoustic wave element disposed on the piezoelectric substrate and having a two-port surface acoustic wave resonator filter having input and output IDTs, a printed circuit board and a conductive bump. In the surface acoustic wave element, one of a pair of interdigital electrodes constituting the input IDT is connected to an output side signal conductive pattern including an input side signal wiring and an input signal terminal. The other one is connected to an input side ground conductive pattern including an input side ground wiring and an input side ground terminal. One of a pair of interdigital electrodes constituting the output IDT is wired to the output side signal conductive pattern including the output side signal wiring and the output signal terminal. The other one is connected to the output side ground conductive pattern including the output side ground wiring and the output side ground terminal. At least one of the input side and output side ground conductive patterns is extended facing to both the input side and output side signal conductive patterns and forms capacitance. The printed circuit board comprises an area thereon the surface acoustic wave element is mounted and terminals corresponding to an input signal terminal, an output signal terminal and a ground terminal of the surface acoustic wave element. The conductive bump connects the input signal terminal, the output signal terminal and the ground terminal of the surface acoustic wave element and the terminals of the printed circuit board.
In the surface acoustic wave element, at least one of the input side and output side ground conductive patterns comprises at least one of an input capacitance formation conductive pattern and an output capacitance formation conductive pattern. The input capacitance formation conductive pattern is part of the ground conductive pattern and is extended facing to the input side signal conductive pattern and the input side signal conductive pattern. The output capacitance formation conductive pattern is part of the ground conductive pattern and is extended facing to the output side signal conductive pattern and the output side signal conductive pattern. Capacitance between the ground conductive pattern and the input side signal conductive pattern and capacitance between the ground conductive pattern and the output side signal conductive pattern may be formed between the signal conductive pattern and the capacitance formation conductive pattern extended facing to the signal conductive pattern. Further, these capacitances of the surface acoustic wave element may be formed of the comb-shaped electrodes or may be formed due to conductor patterns facing through a layer of dielectrics.
For the printed circuit board, a printed wiring board such as for instance a ceramic substrate can be used. By adopting such configuration, the present surface acoustic wave device, while realizing miniaturization of a package due to the flip-chip assembling, without using bonding wire, can improve characteristics out of pass band of the filter, that is, can add a resonant system having a trap in a frequency band for instance several hundreds MHz apart from a pass band. Accordingly, a surface acoustic wave device small in size and excellent in frequency characteristics, particularly suitable for mobile communication instruments, can be realized.
A surface acoustic wave element of the present invention comprises a piezoelectric substrate, a first conductor layer disposed on the piezoelectric substrate, a layer of dielectrics and a second conductor layer. The layer of dielectrics is formed laminated on at least part of the first conductor layer. The second conductor layer is laminated through at least part of the layer of dielectrics in at least part of the area of the first conductor layer.
That is, in the surface acoustic wave element of the present invention, on the first conductor layer disposed on the piezoelectric substrate, through the layer of dielectrics the second conductor layer is disposed to form a capacitance element. The first and second conductor layers are formed in the patterns of for instance surface acoustic wave filter, surface acoustic wave resonator, surface acoustic wave resonator filter, routing electrode or the like. Thereby, a resonant system can be added so as to have a trap in a band different from a pass band of a filter formed in an element.
According to the present invention, without making use of the inductance of the bonding wire as before, a surface acoustic wave element can be assembled due to flip-chip assembling to miniaturize and a trap can be simultaneously formed in a frequency band several hundreds MHz apart from the pass band.
In the present invention, the layer of dielectrics, without restricting to a single layer structure of one dielectrics, can be formed in a mixed layer of a first dielectrics of first permittivity and a second dielectrics of second permittivity or may be formed in a laminate structure thereof. Alternately, three or more kinds of dielectrics of different permittivities may be mixed or laminated to use. Thereby, the magnitude of capacitance being added can be further easily adjusted.
As the dielectrics being used in the present invention, various kinds of dielectrics including for instance silicon oxide (SiOx), silicon nitride (SiNx), silicon oxynitride (SiON) can be used.
In flip-chip assembling, after a conductive bump such as gold bump or the like is disposed on a pad for connection disposed on the piezoelectric substrate, between the bump and the corresponding pad on the printed circuit board, heat, pressure, ultrasonics or the like is inputted to form a solid diffusion layer and to connect. As a result, onto the pad, during connection, large stress is applied. Accordingly, it is preferable to thicken a conductor of the pad portion to strengthen mechanical strength.
In laminating a plurality of conductor layers through layer of dielectrics to form a capacitance element on the piezoelectric substrate, by penetrating the layer of dielectrics to interlayer-connect the first and second conductor layers, reliability of connection with the external due to the conductive bump can be further improved.
Thus, the present surface acoustic wave element may comprise a piezoelectric substrate, a first conductor layer disposed on the piezoelectric substrate, a second conductor layer laminated through at least part of the area of the first conductor layer and a layer of dielectrics, and means for interlayer connecting the first and second conductor layers penetrated through the layer of dielectrics.
On the second conductor layer, a conductive bump may be disposed. Of course, the surface acoustic wave element can be bonding assembled, even in that case reliability in connection being able to improve.
In the surface acoustic wave element and the surface acoustic wave device of the present invention, thus, in the surface acoustic wave element, or between the surface acoustic wave element and the envelope, capacitance can be formed. Due to the capacitance formation, another resonant system different from the resonant system of surface acoustic waves can be added.
Even when the flip-chip assembling is used in assembling the surface acoustic wave element to miniaturize and there is not relatively large inductance due to the wire as in the case of the existing wire bonding, a resonant system can be added, that is a position of a trap can be adjusted at a frequency band for instance several hundreds MHz apart from a pass band. Accordingly, due to the present invention, a surface acoustic wave element and a surface acoustic wave device that are small in size and excellent in attenuation characteristics out of band can be provided.